The spatial expression of Hoxb genes are controlled during vertebrate morphogenesis. Current evidence suggests that there may be a selectivity or directionality in the way that the Hox enhancers influence expression of specific genes. The goal of this proposal is to investigate the global or long range mechanisms important in regulation of Hoxb genes. To approach this problem experimentally, transgenic analysis and targeted mutagenesis in mice will be used to characterize the global aspects of Hox complex regulation and ordered A-P expression. I will achieve this by using a double lacZ and AP reporter system, developed in the host lab, that marks the simultaneous readout of expression from any two genes in the complex. Deletion constructs will be made to examine the impact of specific regulatory regions over a long range on multiple genes marked with the transgenic reporters. This approach will be complemented using Drosophila assays as a means of testing the potential Polycomb Response Elements and chromatin boundary or remodelling elements from the mouse Hoxb complex. Putative functional domains from the mouse complex will be tested in flies to determine if they are capable of functioning as enhancer boundary or insulating elements. The availability of clones from the Hoxb complex of other vertebrates will allow me to examine the degree to which regulatory regions defined by the above assay are generally conserved during vertebrate evolution.